Abstract
The GEOS, Groupe Européen d’Observation Stellaires, is composed of observers living in France, Italy, Spain, Belgium and Switzerland. The main purpose is to give amateur astronomers the opportunity of carrying out scientific analyses in specific fields. Further details can be found at the web site http://www.upv.es/geos/In the past years, GEOS has approached the analysis of visual estimates of variable stars (Ralincourt et al., 1987) in an original manner, obtaining accurate light curves on red semiregulars. Moreover, the collaboration with teams of professional researchers allowed the group to obtain interesting results on the double-mode Cepheid EW Set (Figer et al., 1991), on the Be star OT Gem (Arellano Ferro et al., 1998) and on the eclipsing binary V753 Cyg (Beltraminelli et al., 2000). More recently, several GEOS members have started collecting a large sample of times of maximum brightness of RR Lyr stars in order to build-up a database as extensive as possible. Such a database is decribed below together with the results of a campaign on RR Lyr itself.
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